Http Push

“Because as rapid as the arrival of networked pull media was, the second act - networked push media - is coming even faster. ”

March 1997WIRED Magazine

Thursday, March 11, 2010

PushA 2010 case study with

the NGINX HTTP Push Module,Ruby on Rails, and friends

Luke Melia

Thursday, March 11, 2010

Who’s this guy?

★ VP, Engineering at weplay.com

★ Agilist

★ nyc.rb’er since ~2006

★ Ruby in Practice contributor

★ Interested in startup tech leadership

★ Beach volleyball player

★ Dad

Thursday, March 11, 2010

What’s this talk?★ The goal and the problem

★ A quick survey of solutions

★ About the NGINX HTTP Push Module

★ How to use it with Ruby, by example

★ Gotchyas

★ Q & A

Thursday, March 11, 2010

The Goal★ Immediate encouragement

of positive on-site actions

★ “Points!”

Thursday, March 11, 2010

+10

Thursday, March 11, 2010

Constraints★ Don’t want to figure out points earned

while processing the request (offload it to a background work queue)

★ Do want to inform about points earned through another user’s actions

★ Don’t want to wait for a second page load

Thursday, March 11, 2010

Pure pushdoesn’t exist

on the open web

Thursday, March 11, 2010

Push-likesolutions

XMPP

Comet

WebSockets

StreamingThursday, March 11, 2010

Streaming

★ Don’t close the connection after sending down the page

★ multipart/x-mixed-replace★ Supported in non-Microsoft

browsers only

Thursday, March 11, 2010

★ Designed for presence and messaging★ Browsers don’t speak XMPP natively★ BOSH★ Hemlock: Flex + ejabberd, by NYC’s

Mint Digital

XMPP

Thursday, March 11, 2010

Comet

★ Push data over a long held Ajax request using browser-native technologies

★ Bayeaux protocol★ Long-polling Ajax

Thursday, March 11, 2010

WebSockets

★ HTML 5★ Full-duplex single socket connection

between browser and server★ ex: ws://websockets.org:8787★ very limited browser support today

Thursday, March 11, 2010

XMPP

Comet

WebSockets

StreamingThursday, March 11, 2010

Servers

NGINX HTTP Push Module

Faye

Tornado

ejabberd

Orbited

Diesel

CrampRainbows!

Sunshowers

Juggernaut

Thursday, March 11, 2010

NGINX HTTP Push Module

★ Turns NGINX into a Comet server

★ “A useful tool with a boring name.”

★ By Leo P

★ http://pushmodule.slact.net/

★ Currently at 0.692β

Thursday, March 11, 2010

Basic HTTP PushRelay Protocol

★ Subscriber locations

★ HTTP GET with channel ID

★ Publisher locations

★ HTTP POST with channel ID

★ POSTed data is passed through, becoming the response to the subscriber’s GET

Thursday, March 11, 2010

NGINX

Subscriber endpoint

Publisher endpoint

End User

BACK-END

PROCESS

Diagramming the simple case

1. HTTP GET

2. HTTP POST

3. POST BODYIS ROUTED BYCHANNEL ID

4. RESPONSE ISDATA FROMPOST BODY

Thursday, March 11, 2010

ChannelConcurrency Styles

★Broadcast★Last-in, first-out★ First-in, last-out

Thursday, March 11, 2010

Subscriber config

# public long‐polling endpoint

location /rt/notifications {

  push_subscriber;

  set $push_channel_id $arg_id;

  push_subscriber_concurrency last;

}

Thursday, March 11, 2010

# internal publish endpoint# (keep it private / protected)location /rt/publish {  push_publisher;  set $push_channel_id $arg_id;  push_store_messages on;  push_message_timeout 5m;  push_max_message_buffer_length 5;  push_min_message_buffer_length 0;  push_delete_oldest_received_message on;}

Publisher config

Thursday, March 11, 2010

NGINX

Subscriber endpoint

Publisher endpoint

End User

BACK-END

PROCESS

Diagram with storage

3. HTTP GET

1. HTTP POST

5. RESPONSE ISDATA FROM

QUEUE

Queue

2. POST BODYIS QUEUED

BY CHANNEL ID

4. MESSAGEIS RETRIEVEDFROM QUEUE

BY CHANNEL ID

Thursday, March 11, 2010

Code it up.

Thursday, March 11, 2010

Client-side Gotchas

★ Javascript blocking

★ Put it in an iframe

★ Per domain connection limit

★ use subdomain, with JSONP

Thursday, March 11, 2010

Server-side Gotchas★ “Too many open connections”

★ Reduce worker_connections to less than ulimit -n

★ Increase worker_processes to give you enough total connection to serve your users

★ Ours: worker_processes 24 worker_connections 960

Thursday, March 11, 2010

Testing

★ Fake Publisher for in-memory cucumber scenarios

★ Run selenium scenarios through NGINX to incorporate actual push module behavior

Thursday, March 11, 2010

NGINX Configuration Management

★Template it★Version it★Automate it

Thursday, March 11, 2010

The Future

★ Multiplexing: subscribe to more than one channel

★ Use Redis as a message store

★ Convention-based approach for raising javascript events

Thursday, March 11, 2010

Questions?

Thursday, March 11, 2010